1. Field of Invention
The present invention relates to a locking device for a tire mounted on a wheel rim to optimize dynamic balancing of a tired wheel, particularly, but not exclusively, suitable for tire balancing machines, tire assembling-release machines and the like.
Balancing of a tired wheel is a delicate operation which in general has to be carried out with care by an operator as balancing could affect the road-holding of the vehicle and thus the safety of the passengers. As a matter of fact, a non-optimum balancing could result in vibrations and resonance phenomenons being caused owing to unbalanced forces or force resultants with respect during standard operation of the vehicle.
As it is known, the aforesaid forces are generated when a tired wheel is rotated about its axis of rotation owing to:                uneven distribution of the wheel rim and tire mass of the tired wheel with respect to its axis of rotation;        uneven distribution of the wheel rim mass due to misalignment between the inertial axis of rotation of the wheel rim and the axis of rotation of the tired wheel; and        uneven distribution of the tire mass due to misalignment between the inertial axis of rotation of the tire and the axis of rotation of the tired wheel, e.g. owing to bad mounting of the tire.        
2. Description of Related Art
Tired wheel balancing is usually carried out by means of a balancing machine comprising a rotatable support which can rotate about an horizontal or vertical axis of rotation and is provided, e.g. with jaws for engaging the tired wheel rim or with a grip headstock comprising a number of expansion arms and being rotatable about the same axis of rotation, or with a fixing flange having a pneumatic threaded-hub system. When the tired wheel is rotated, by the rotatable support, any mass imbalance with respect to the axis of rotation is detected by suitable sensor means, e.g. magnetic, optical or pressure sensor means, suitably connected to an electronic computer unit adapted to store and process data forwarded thereto. At this point, the standard procedure adopted to re-balance a tired wheel provides, as known, trying to eliminate such unbalances by adding sufficient additional masse-balance weights at suitably chosen positions. For correct positioning of such masses in most recent balancing machines use is made of optical pointers (lasers) controlled by the electronic computer that had previously reckoned the precise positioning of the mass-balance weights along the wheel rim edge.
When the weight of such additional masse-balance weights, however, exceeds a predetermined value, e.g. about 50 g, it is usually preferable to cause the tire to rotate about the axis of rotation of the tired wheel with respect to the wheel rim (or viceversa), so as to compensate, at least to a large extent, mass unbalances due to the wheel rim for those caused by the tire.
Such a tire rotation about the axis of rotation of the tired wheel is carried out as follows:                the tired wheel is fixed on a rotatable support of a tire assembling-disassembling machine;        the wheel tire is deflated and its bead is released; and        the tire or the wheel rim is rotated, through an angle of about 180 degrees, with respect to the wheel rim or the tire, respectively.        
To cause the tire to effect an angular rotation through about 180 degrees with respect to the wheel rim, no matter what tired-wheel maintenance machine is used, the operator usually acts on a suitable manually operated control, e.g. a pedal located on the base of the maintenance machine, thereby setting in rotation the rotatable support on which the wheel rim is secured. The wheel rim is thus set in rotation, and the tire is, in turn, caused to rotate owing to friction between the wheel rim edge and the tire bead.
The problem to be faced by the operator is to be able to lock or slow down any uncontrolled rotation of the tire that, due to friction, is dragged by the wheel rim secured to the rotatable support. Up to now, the operator has resorted to expedients, such as manually rotating the tire with respect to the wheel rim or manually slowing down the tire possibly by using a tool inserted between tire and wheel rim, while the maintenance machine causes the wheel rim to rotate. Such expedients are obviously troublesome and totally unsatisfactory.
This situation is even worse when a tire has a lowered bead or profile, as in this case the contact area between tire internal bead or edge and the wheel rim edge is much more extended than that provided in a standard tire, and thus the operator's task becomes much more difficult as higher strength is to be exerted in this operation in trying to stop or slow down tire rotation with respect to the wheel rim rotation. Moreover, with lowered profile tires use is made of alloy wheel rims that inevitably become damaged or at least scratched when tools are inserted between wheel rim and tire.
A further problem is faced when assembling and disassembling a special wheel tire. As a matter of fact, in order to mount a tire on a wheel rim the tire bead must get over and beyond the wheel rim edge, and thus the operator does force a portion of the tire bead by means of a suitable tool to exceed the wheel rim edge, after which care should be taken in gradually forcing the remaining tire bead to move beyond the wheel rim edge. Especially when dealing with wheels of large dimensions, e.g. truck or lorry wheels, the bead resistance to deformation is quite substantial, and thus it is quite difficult for the operator to accomplish the necessary steps to assembly or disassembly a tire.